This project focuses on the development of air breathing organs in anabantoid fishes as a model system. The goal is to perform a multidisciplinary analysis of the origin of novel structures in development and evolution. These fish possess unique paired branchial structures for aerial respiration. The key to studying this anatomical novelty is the control of its induction. Development of air breathing organs requires access to the water surface; without access, development of the organ is arrested. The experimental control of induction provides a unique opportunity to probe the evolutionary origin and morphogenesis of an organ by producing large numbers of experimental animals suitable for differential molecular analysis. Following the histological characterization of the air breathing organ development, the genes and their pattern of expression after induction of the air breathing organ will be identified with representational difference analysis of cDNA. Development and evolution differ in approach and the time scale involved, but, because they share a central focus on the process of change, may provide complementary information about the morphogenesis and the origin of new features. At a fundamental level, either novel genes and/or pre- existing genes coopted and expressed in a novel pattern react to the inductive signal of an air breath. These genes form the basis of the morphogenesis of the air breathing organ and provide clues about its evolutionary origin. Characterizing those genes will form the basis of future research on their evolutionary precursors or on changes in patterns of gene expression leading to the origin of novel structures and the evolution of air breathing.